Small dumbbells are often used in enhancing the muscular fitness of a user's arm, without significant muscular fatigue. However, these dumbbells still eventually generate some arm numbness, do not permit articulation of the fingers nor of the whole hand, and still bring some fatigue level after a while.
U.S. Pat. No 3,069,161 issued Dec. 18, 1962 to James MELCHIONA, does disclose a hand exerciser consisting of two balls which are interconnected by a straight connector member. Connector member can be twisted, whereby the balls are partly rotatable relative to one another.
U.S. Pat. No. 4,984,784 issued 15 Jan. 1991 to Arthur BAILEY discloses a hand exerciser consisting of a pair of balls interconnected by a magnet. This magnet allows translational as well as relative rotational motion of the balls.
U.S. Pat. No. 4,577,858 issued 25 Mar. 1986 to Masanobu HIGAMI discloses a fingertip exerciser, consisting of two balls that are interconnected to one another by a quadrangular open frame, wherein the balls can rotate independently of one another orthogonally to the interconnection radial axis of the connector frame.